The following geometrical objects in SPRAY may be covered by simple pre-defined interfaces or user-defined interfaces (details of interfaces have been given above). The objects are divided into two classes: Some (like spheres or solid cylinders) completely enclose a certain volume with their surface. These are called Closed volumes. Others (like rectangles or circles) are referred to as 'Open structures'. These objects cannot enclose a volume alone.

'Open' structures:

Closed volumes